This invention relates to accelerometers in general and more particularly to an improved forced rebalanced accelerometer utilizing a spherical proof mass and fluid pressure pulses for balancing.
Conventional accelerometers normally use a proof mass supported on a pendulum or the like. In order to obtain rebalancing forces torquer coils are used. As an example of such an accelerometer see U.S. Pat. No. 3,680,393.
Although such accelerometers operate quite well they do have certain disadvantages. Because of the flexure-like pendulum supports there is a mechanical null which is defined as the pendulum position at which flexure torques are zero. Unfortunately, this mechanical null position does not always coincide with the electrical null position which is defined as the pendulum position at which the pickoff electrical output is zero. Due to this lack of coincidence between the two nulls there is bias which is accompanied by bias instability errors caused by mechanical and electrical null position shifts. Furthermore, in order to obtain proper operations in a conventional accelerometer very precise current pulses, both in duration and amplitude, are required to maintain a constant scale factor [dynes/amp]. In order to maintain these pulse characteristics, solid state analog electronic components are utilized. Such solid state components when operated in an analog fashion are susceptible to nuclear radiation to a large degree. This susceptibility exceeds the susceptibility when such semiconductor devices are used in a digital or switching mode. As a result, circuits used with conventional accelerometers are susceptible to radiation and either cannot be used for or must specially designed if to be used in a radiation environment.
Thus, the need for an improved accelerometer which avoids the difficulties associated with conventional prior art accelerometers becomes evident.